System including a seamless lens cover and related methods

ABSTRACT

A seamless lens cover, and methods of forming such a seamless lens cover. The cap structure that covers a camera of a rotating panoramic camera system includes a seamless lens cover through which images are obtained by the camera. The cap structure may be injection molded at an initial lens cover thickness, and then a portion of the as molded initial lens cover thickness may be removed (e.g., by machining away) to achieve the final desired thickness. By such a method, the lens cover may be injection molded at thicknesses suitable for injection molding (e.g., about 0.06 to about 0.1 inch), after which most of the thickness may be machined away, to provide a seamless lens cover having a thickness of less than about 0.015 inch, exhibiting at least 60% transmittance to the thermal spectrum, no lensing characteristics, and no curvature effect.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/456,329 filed Aug. 11, 2014, titled “SYSTEM INCLUDING A SEAMLESS LENSCOVER AND RELATED METHODS”, now U.S. Pat. No. 9,348,196, which claimsthe benefit of U.S. Provisional Application No. 61/864,196 filed Aug. 9,2013, titled “METHODS FOR ANALYZING THERMAL IMAGE DATA USING A PLURALITYOF VIRTUAL DEVICES, CORRELATING DEPTH VALUES TO IMAGE PIXELS, AND ASYSTEM INCLUDING A SEAMLESS LENS COVER”. Each of the foregoing isincorporated herein by reference in its entirety.

BACKGROUND 1. The Field of the Invention

The present invention is in the field of automated camera systemscapable of taking images at a plurality of stop positions (e.g., in apanorama), and in particular a seamless lens cover for use therewith.

2. The Relevant Technology

Panoramic images can be created by an array of wide angle cameras thattogether create up to a 360 degree field of view or by one camera with afish eye lens or other panoramic mirror that allows for a continuous“mirror ball” image that is later flattened out by computer. Theseimages are limited in their ability to provide detail necessary to beuseful for video surveillance because the sensors are stretched overwide fields of view (sometimes a full 360 degrees).

A relatively new means of capturing thermal panoramic images is bycontinuously spinning a cryogenically cooled thermal sensor or otherhigh speed camera at less than 60 RPM and processing the images from thecamera with a computer where they are stitched together and analyzed.These cryogenically cooled sensors have the ability to capture images injust a few nanoseconds, which allows them to produce near real timevideo. However, these cooled sensors are power hungry and expensive,making them impractical in many applications. In addition, the highspeed cameras have very large lighting requirements making them of verylimited use in other than full daylight conditions.

Even with existing advancements in the art, there still exists a needfor improved camera systems.

The subject matter claimed herein is not limited to embodiments thatsolve any disadvantages or that operate only in environments such asthose described above. Rather, this background is only provided toillustrate one exemplary technology area where some embodimentsdescribed herein may be practiced.

SUMMARY

Implementations of the present invention are directed to camera systemsincluding a cap structure that covers the camera. The cap structureincludes a seamless lens cover. The present invention is also directedto related methods of use for the system. The invention also relates tomethods of manufacturing the seamless lens cover. The seamless lenscover may comprise a cylindrical sidewall of the cap structure in whichthe cylindrical sidewall has a finished thickness of less than 0.05inch, less than 0.025 inch, or less than 0.015 inch, and in which thelens cover includes no seams. By way of example, the sidewall thatserves as a lens cover may have a finished thickness of about 0.009 inchto about 0.013 inch. The cap structure may be injection molded orotherwise provided with the sidewall at an initial thickness that isgreater than the desired final thickness. The thickness of thecylindrical sidewall may then be machined or otherwise worked to removea portion of the initial thickness of the sidewall to achieve thedesired final thickness. In an embodiment, the as provided (e.g.,injection molded), initial thickness may be about 0.1 inch, or from 0.06to 0.1 inch.

These and other advantages and features of the present invention willbecome more fully apparent from the following description and appendedclaims, or may be learned by the practice of the invention as set forthhereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to describe the manner in which the above-recited and otheradvantages and features can be obtained, a more particular descriptionof the subject matter briefly described above will be rendered byreference to specific embodiments which are illustrated in the appendeddrawings. Understanding that these drawings depict only typicalembodiments and are not therefore to be considered to be limiting inscope, embodiments will be described and explained with additionalspecificity and detail through the use of the accompanying drawings inwhich:

FIG. 1 illustrates a schematic block diagram showing an exemplary camerasystem in which the seamless lens cover may be employed.

FIG. 2 is a flow diagram illustrating an exemplary method by which thecap structure including the seamless lens cover may be manufactured.

FIG. 3A is a perspective view of an exemplary camera system including acap structure providing a seamless lens cover.

FIG. 3B is an exploded perspective view illustrating the cap structurein greater detail.

FIG. 4A is a perspective side view of an exemplary cap structure asinitially injection molded, having a thick sidewall to be subsequentlythinned.

FIG. 4B is a cross-sectional view through the injection molded capstructure of FIG. 4A.

FIG. 4C is a cross-sectional view similar to that of FIG. 4B, but afterthe sidewall which serves as the lens cover has been thinned by removinga portion of the sidewall thickness.

FIG. 4D illustrates the cap structure after the sidewall has beenthinned, and the thinned sidewall has been sanded.

FIG. 4E illustrates the cap structure after the sidewall has beenpolished, providing the finished surface that serves as the seamlesslens cover.

FIG. 5 illustrates how the cap structure of FIGS. 4A-4B may be placedover a mandrel and machined using a lathe cutting tool to remove aportion of the thickness of the sidewall that becomes the seamless lenscover.

FIG. 6 illustrates how the cap structure of FIG. 4D may be placed aver amandrel and polished using a plurality of differently configured foampads to achieve the final surface finish for the sidewall which servesas the seamless lens cover.

DETAILED DESCRIPTION I. Introduction

The present invention is directed to methods for forming a seamless lenscover for a camera, e.g., a cap structure including such a lens cover,where the cap structure covers or caps a camera of a camera system. Thecap structure includes the seamless lens cover for the camera,protecting the camera and other internal structure under the capstructure from the elements (e.g., such systems are typically placedoutdoors), while at the same time allowing the camera of the system tocapture images (e.g., thermal images in the infrared spectrum—e.g.,about 8000 nm to about 14000 nm) through the seamless lens cover,without any degradation of image quality associated with a seam. Becausethe lens cover is seamless, 360° image capture without any degradationdue to a seam is possible. In addition, the lens cover can be formed soas to exhibit no significant lensing characteristics (i.e., minimal tono artifacts introduced by the presence of the lens cover, and nosignificant curvature effect (i.e., no significant distortion of theimage due to the curvature of the lens cover). The lens may exhibit someloss in transmission (e.g., at least about 60% transmission, such as65-70% transmission), but exhibits sufficient transmission through theseamless lens cover to provide excellent results. In addition to theabove characteristics, the lens cover exhibits minimal reflection (e.g.,particularly at the exterior surface), and low diffraction of incidentwavelengths.

The method by which the seamless lens cover is formed (e.g., as part ofan overall cap structure) may include providing the cap structure withan initial lens cover thickness that is greater than the final desiredthickness. For example, the cap structure may include a generallycylindrical sidewall that serves as the lens cover. The lens cover maybe injection molded or otherwise formed at an initial “thick” thicknesswithout any seams. A portion of the initial lens cover thickness isremoved (e.g., by machining it away) to achieve the desired finalthickness. In addition to removal by machining, the lens cover may besanded (e.g., wet sanded) and polished (e.g., wet polished) aftermachining to achieve the final desired thickness, smoothness,transmission, and other optical characteristics.

The seamless lens cover and associated method of manufacture areparticularly advantageous. For example, the inventors were toldrepeatedly by those of skill in the art that it would be impossible toinjection mold, thermoform, or otherwise form or mold the desired capstructure including a seamless lens cover having the needed thicknesscharacteristics so as to provide the desired performancecharacteristics. For example, the final desired thickness in thesidewall that serves as the lens cover may be less than 0.025 inch, nomore than about 0.015 inch, or between about 0.009 inch and 0.013 inch.At such thin cross-sections, it proved a practical impossibility toinjection mold the cap structure including the seamless lens cover.Injection molding would be particularly advantageous as it would allowthe formed cap structure to be a single integral piece, formed of asingle integral piece of material.

In testing to determine if such injection molding were possible (evenafter being told it was a practical impossibility by those of skill inthe art), the inventors found that trying to injection mold the materialwas not possible. For example, when using a thermoplastic material suchas a polyolefin, e.g., polyethylene, such as an ultra-high molecularweight polyethylene (UHMWPE), it was practically impossible to preventstreaking or burning within the thin-walled seamless lens portion of thecap structure due to temperature issues, even while operating theinjection molding apparatus at the highest possible pressures. Inaddition to these problems, the thickness consistency within theseamless lens sidewall portion was much too eccentric and variable, thesidewall thickness of the lens cover was still too thick, and otherproblems were repeatedly encountered. As a result, the rejection ratewas about 98% (i.e., only 1 in 50 manufactured parts were acceptable inmost regards, other than the sidewall was still too thick, eccentric,etc.). As a result, none of the product produced in injection moldingtesting actually met the desired specifications.

The inventor also attempted formation through thermoforming. Theinventor was told repeatedly that thermoforming structures (e.g.,disposable plastic cups) can be practical where the taper of thesidewall is at least 5°. The cap structure as illustrated includes notaper, but the sidewall that serves as the lens cover is vertical inuse. The inventor was told that because there was no angle or taper ofat least 5° it would not be possible to thermoform the cap structure.The thermoforming tests were also unsuccessful. The fact that the capstructure includes no taper is beneficial from a performanceperspective, as the radial distance of the sidewall serving as the lenscover to the camera is the same, independent of the location along theheight of the sidewall. For example, if a taper were provided, thesidewall would be inclined somewhat off relative to vertical, so that alocation near the top of the sidewall would exhibit a different distancefrom the camera as compared to a location near the bottom of thesidewall. Such differences would be expected to introduced artifactsinto the captured images. Thus, while beneficial from a performanceperspective, the lack of any significant tape (e.g., no taper, incline,or slope at all—but rather a vertical surface) makes it not possible toform the cap structure including the lens cover sidewall fromthermoforming.

Thus, as described, it was not possible as a practical matter tofabricate the cap structure including a sidewall that could serve as alens cover using injection molding or thermoforming. The inventordeveloped an alternative method of fabrication which has surprisinglybeen found to allow production of the desired parts, with acceptably lowrejection rates (e.g., less than 10%, less than 5%, less than 2%, orless than 1%), all while providing the desired seamless lens cover thatis an integral part of a cap structure that may be injection molded as asingle piece of material, without any seams. In order to achieve this,the cap structure is provided (e.g., through injection molding) in aninitial thickness with respect to the sidewall that will eventuallyserve as the lens cover. At these initial thicknesses, injection moldingis readily achievable. The sidewall is subsequently worked (e.g.,machined), to achieve the desired thicknesses in the sidewall of the capstructure, so as to result in a seamless lens cover having the variousdesired characteristics.

Upon seeing the finished product, others of skill in the art stillwonder how the present inventor could have ever produced such astructure, particularly in a manner that would allow large scalemanufacture with consistent quality and low to no rejection rates forparts. For example, their exclamation is often “how did you do that!?”.

II. Exemplary Systems Including a Seamless Lens Cover and Methods ofManufacture

FIG. 1 illustrates a block diagram for an exemplary camera system 100 inwhich the seamless lens cover described herein may be employed. Camerasystem 100 allows camera 102 (e.g., a thermal imaging camera) to rotateup to a full 360° around a fixed-axis. The full revolution comprises anumber of positions corresponding to “stops” where it is desired that animage be captured. The spectrum captured may be long wavelength infrared(LWIR), from about 8-14 μm (8000 nm to about 14,000 nm). Of course, itmay be possible to employ concepts disclosed herein within systemsconfigured to capture and use image data based on other spectrums (e.g.,visible light, or higher or lower wavelengths). Thus, the sensor of thecamera may be configured to capture LWIR wavelengths, visible lightwavelengths, or other wavelengths or light (i.e., electromagneticradiation). Capture of the LWIR spectrum is particularly beneficialbecause it can “see” through darkness, making it suitable for use anytime of day or night, and it less affected by fog, clouds, or otherfeatures that might obscure imaging based on the visible spectrum. Asthe camera rotates, it is periodically stopped at designated stoppositions, where the camera is momentarily stopped and an image iscaptured. The camera then rotates to the next stop position, obtainingthe next image, and so forth, through the full revolution. The cameramay appear to rotate continuously, because the dwell or stop timesassociated with each stop position may be so short (e.g., about 60 ns).Additional details of the camera system and its use are disclosed in theabove reference provisional application, and PCT Patent ApplicationPCT/US14/49986 filed Aug. 6, 2014, herein incorporated by reference inits entirety. Additional details of such systems are disclosed in PCTPatent Application Serial No. PCT/US/2014/033539, PCT Patent ApplicationSerial No. PCT/US/2014/033547, and U.S. Pat. No. 8,773,503, each ofwhich is herein incorporated by reference in its entirety.

A seamless lens may form part of a cap structure that covers orencapsulates the camera 102, so that it is protected from the outdoorelements, while being able to capture images across a full 360° panoramawithout a typically present seam negatively affecting image quality.FIG. 2 illustrates an exemplary method S10 by which such a seamless lensmay be formed. For example, at S12, the cap structure may be provided.Such a cap structure may be injection molded or otherwise formed,provided in a condition where the sidewall (e.g., a closed generallycylindrical loop) that serves as the lens cover is of an initial asmolded thickness (e.g., about 0.1 inch to about 0.06 inch) that isgreater than the final desired thickness (e.g., about 0.009 inch toabout 0.013 inch). At S14, a portion of the initial cover thickness isremoved (e.g., machined away), so as to achieve the desired finalthickness. The resulting surface may be sanded (S16) and/or polished(S18) to provide a finished smooth surface having the desiredcharacteristics (e.g., high transmittance, low reflectance, lowdiffusion, good durability, etc.)

FIGS. 3A and 3B show perspective and exploded views, respectively, of anexemplary camera system 100 including the cap structure 106 with theseamless lens cover 112. System 100 includes a camera 102 mounted on anindexing mechanism 104, which rotates the camera 102 through theplurality of stop positions. System 100 further may include the variousdesired electronic processors for sorting, analyzing, storing, andotherwise using or manipulating the image data and other relevant dataobtained with system 100. As described in the referenced relatedapplications, the images may specifically not be stitched together tocreate a panoramic image, but stored and processed individually (e.g.,as if a stationary camera were positioned at each stop position). Thelack of such stitching greatly reduces the power and computingrequirements of the system.

As described herein, system 100 farther includes a cap structure 106that covers camera 102 of system 100. Cap structure 106 may be of aclosed shape, so as to fully circle about camera 102. In an embodiment,it may be generally cylindrical in shape, including a top end 108 (e.g.,closed) and an open bottom end 110, allowing cap structure 106 to beplaced over camera 102, encapsulating and protecting camera 102 therein.Cap structure 106 includes a sidewall 112, which serves as the lenscover through which camera images are obtained. Sidewall 112 may definethe outer perimeter or diameter of a hollow cylindrical body, where thecylindrical wall includes no seams. Sidewall 112, also referred toherein as lens cover 112, is seamless, so as to not include any seams asa result of the molding or other fabrication process. In an embodiment,as shown, lens cover 112 may be generally cylindrical in shape, forminga closed loop shape (e.g., circling around the camera 102). As describedabove, sidewall 112 may be vertical in use, rather than including anytaper, slope, or incline (referred to herein collectively as taper forsimplicity). In another embodiment, minimal taper could be present(e.g., less than 4°, less than 3°, less than 2°, or less than 1°),although no taper is preferred, as described above. As such, thesidewall 112 may be characterized as being substantially vertical.

Such a lens cover 112 is particularly well suited for applications inwhich a full 360° panorama is to be under surveillance. Of course, lessthan a full 360° may be monitored, and in such embodiments a seamlesslens cover may not be necessary (e.g., the seam could be placed where nomonitoring is done). In other embodiments, even though less than a full360° may be monitored, a seamless lens cover extending the full 360° maybe employed. For example, the system could be programmed or otherwiseset up and configured to monitor less than 360°, even though the systemmay be capable of monitoring the full 360°.

The cap structure 106 may be coupled to a top cap 114 (e.g., a plastic,other material, rubber or other elastomeric cap) placed over a topportion 116 of structure 106, above lens cover 112, and adjacent closedtop end 108. In another embodiment top end 108 may not be fully closed,but closure and sealing of the internal space may be provided by cap114. As shown, the top portion 116 over which cap 114 is placed may beof a width (e.g., diameter) that is less than the width (e.g., diameter)of lens cover portion 112. Adjacent bottom end 110, a thickened flange118 may be provided, e.g., including structure for securing capstructure 106 to the adjacent portion of system 100. For example, flange118 may be outwardly flared, extending radially outward from the bottomof sidewall 112, adjacent bottom end 110. Flange 118 may include threads120 or other coupling structure for engagement with correspondingcoupling structure of system 100 to which cap structure 106 is to besecured. In the illustrated embodiment, outwardly flared flange 118further includes an annular groove 122 into which a sealing O-ring 124may be placed. Threads 120 and groove 122 may be machined into bottomend 110 after injection molding, or one or both may be formed duringinjection molding, as desired.

FIGS. 4A-4E progressively illustrate how the as provided (e.g.,injection molded) cap structure 106 may be altered from its as providedcondition so as to provide a sidewall 112 that is sufficiently thin toserve as the seamless lens cover. For example, FIGS. 4A and 4Billustrate perspective and cross-sectional views, respectively, of capstructure 106, as provided (e.g., as injection molded). For example,sidewall 112 (and optionally adjacent top portion 116) may be initiallymolded at a thickness at which injection molding is practical. Forexample, the initial thickness of sidewall lens cover 112 may be aboutfrom about 0.06 inch to about 0.1 inch), e.g., about 60 thousandths ofan inch thick (i.e., 0.060 inch). At such thicknesses for the dimensionsof the cap structure (e.g., about 2.5 to about 3 inches in diameter),molding of such a structure is well within the capabilities of a typicalinjection molding apparatus. By injection molding, no seams are presentwithin sidewall 112, as one circles the perimeter thereof.

Sidewall 112 may be cylindrical, rather than cone or truncated coneshaped—which would include a tapered sidewall, as described above. Forexample, the sidewall 112 may include no taper, less than 1% taper, lessthan 2%, less than 3%, or less than 4% taper. Sidewall 112 may bereferred to as being a substantially cylindrical and substantiallyvertical sidewall, in this respect. Because of the lack of at least a 5%taper, the inventor was told repeatedly that it would not be possible toform such a structure through thermoforming.

Once molded at such an initial thickness, from a suitable thermoplasticmaterial (e.g., ultra-high molecular weight polyethylene “UHMWPE”) thesidewall 112 appears opaque, and cannot readily serve as a lens coverthrough which thermal images can be captured, as the transmittance ismuch too low. In order to alter the sidewall 112 so that it could beused as a seamless lens cover, most of the material thickness ofsidewall 112 is removed. For example, the sidewall 112 may be reduced inthickness to about 0.009 inch to about 0.013 inch. At this thickness,sidewall 112 exhibits transmission characteristics of about 65 to about70% (e.g., at least 60%) relative to the desired LWIR wavelengths. Inaddition, the portion of sidewall 112 may be removed and finished in amanner that the finished product exhibits no substantial lensingcharacteristics or curvature effects due to the presence of the lenscover 112.

In addition to the described transmission characteristics, the finishedsurface of sidewall 112 that serves as the seamless lens cover is smoothto the point of being non-diffractive relative to the desiredwavelengths. In addition, it exhibits limited, if any reflection. It isbelieved that the machined and polished surface of sidewall 112 exhibitsa reflection that is no more than about 10%, or no more than 5% withrespect to the target wavelengths. For example, reflectance may be nomore than 30%, no more than 25%, no more than 20%, no more than 15%, nomore than 10%, no more than 5%, no more than 3%, or no more than 1%.Diffraction may be similarly low. As a result, the surface providesminimal interference and artifacts as the wavelengths of interest passthere-through and are captured by camera 102.

The portion of sidewall 112 to be removed may be removed by machining,although this is a relatively delicate operation, as the UHMWPE exhibitsvery long molecular chain lengths. In other words, its micro-structureis such that it tends to want to tear out in chunks, strips or chains,rather than be removed with precision, in minimal thickness andportions, progressively.

FIG. 5 schematically illustrates an exemplary apparatus for performingthis step of removing a portion of the thickness of sidewall 112,without tearing out sections of sidewall 112, as removed portions ripout adjacent sections due to the characteristics of the UHMWPE. Suchripping or tearing destroys surface 112. For example, the as providedcap structure 106 is placed over a mandrel 126. Mandrel 126 is rotatedat relatively high speed (e.g., from about 1000 RPM to about 1800 RPM,or from about 1200 to about 1500 RPM), referring to arrow B. Rotationmay be clockwise or counterclockwise, depending on the location ofcutting tool 128 and other factors.

Because of the high rotational speed of mandrel 126, at least sidewall112 actually lifts off mandrel 126, creating a space or gap betweensidewall 112 and mandrel 126. Other portions of the cap structure 106may continue to contact and be secured to mandrel 126 so that structure106 continues to rotate with mandrel 126. As mandrel 126 rotates capstructure 106, sidewall 112 is contacted with a cutting tool (e.g., aCNC lathe blade 128) which progressively cuts away very small portionsof the exterior of sidewall 112, as shown in FIG. 5. The feed rate atwhich cutting tool 128 progresses axially (arrow A) along the height ofsidewall 112 may be such that it may take less than about 10 seconds foreach pass (e.g., about 5 seconds to about 10 seconds, or about 5 secondsto about 8 seconds). For example, if the height to be machined is fromabout 3 cm to about 5 cm, the axial feed rate may be from about 3 ministo about 10 mm/s, or from about 3 mm/s to about 6 mm/s.

In an embodiment, multiple passes of cutting tool 128 may be used toachieve the desired thickness at the end of the machining step. Forexample, this may be helpful to counteract the tendency of the materialto tear out, rather than be removed cleanly, at only the depth of cut.For example, 3 to 4 passes of cutting tool 128 may be employed to removethat portion of the thickness of sidewall 112 to be removed. Forexample, the final pass may be configured to remove from about 0.005inch to about 0.03 inch, from about 0.010 inch to about 0.015 inch, orabout 0.010 inch to about 0.012 inch in thickness from sidewall 112. Theprevious passes may be configured to remove approximately equal portionsof thickness, relative to one another.

For example, where the initial as molded thickness of sidewall 112 isabout 0.060 inch, and the final desired thickness is from about 0.009inch to about 0.013 inch (e.g., 0.0010 inch), and the thickness removedin the final pass is from about 0.010 to about 0.012 inch (e.g., 0.010inch), where 4 passes total are employed, the first through third passesmay each remove equal amounts (e.g., about 0.013 inch) of the thicknessof sidewall 112. Where only 3 passes total are employed, and the finalpass removes 0.010 to about 0.012 inch, the first and second passes mayeach remove about 0.02 inch.

The subsequent sanding and polishing steps may remove little if any bulkthickness from sidewall 112, rather serving to smooth the surface to thedesired smoothness for the desired high transmittance, low reflectance,and low diffraction characteristics. In other words, the sanding andpolishing may remove protrusions or roughness from the surface, bringingthe higher prominent surfaces down. For example, the sanding andpolishing steps may remove less than 0.001 inch in thickness fromsidewall 112, if removing any of the bulk thickness at all.

The lathe blade or other cutting tool 128 is very sharp in order tominimize the tendency of the material to tear out, rather than becleanly cut, at the desired depth. The tool sharpness in combinationwith the progressive removal of the thickness (e.g., in portions of fromabout 0.005 inch to about 0.03 inch, or from about 0.01 inch to about0.02 inch in a pass) minimizes the otherwise prevalent tendency of thematerial (e.g., UHMWPE) to tear out, rather than being cut. Commerciallyavailable lathe cutting tools (e.g., formed of high hardness metalcarbide materials) are suitable for use. Such tools are available fromMitsubishi under the name MITSUBISHI CARBIDE. In addition to the toolsharpness, the cutting tool is of high precision (e.g., use of a 2ten-thousandths (0.0002 inch) precision tool). Lubricant and/or coolantmay be applied during the machining step to lubricate and cool sidewall112 and cutting tool 128.

Top portion 116 may also be thinned along with sidewall if desired. Ofcourse, this may not generally be necessary, as such portions do notserve as a lens cover through which the LWIR wavelengths are transmittedand captured by camera 102.

After the machining operation, the cap structure 106 may appear as inFIG. 4C, having a substantially thinner sidewall 112 than previously(FIG. 4B). For example, at least about 50%, at least about 75%, or about80% to about 85% of the thickness of side-wall 112 may have beenremoved. At this thickness, the sidewall 112 may appear somewhattranslucent, but may not yet exhibit transmittance characteristics thatare as high as the finished surface of FIG. 4E, e.g., due to surfaceroughness. Once the machining operation is completed, the surface ofsidewall 112 may be wet sanded (e.g., with application of lots of wateror other lubricant) using a very fine grit sandpaper (e.g., 1000 grit).FIG. 4D illustrates how such a sanded texture 130 may result. Such finesanding may begin to further smooth the lens cover surface 112, removingsome of the more prominent “high” surface features. Sanding may beperformed across the grain.

Once sanded, surface 112 is ready for polishing. FIG. 6 schematicallyillustrates how such polishing may proceed. Polishing further smoothesthe surface of sidewall 112, to achieve the final desired very smoothsurface finish, having the desired high transmittance, low reflectance,and low diffraction characteristics. No further treatment or coating ofsurface 112 is needed, although if desired, coatings (e.g., to furtherlower reflectance, diffraction, etc.) could be applied, if desired. Itis advantageous that the UHMWPE material alone (without any suchcoatings) provides the desired characteristics, and is sufficientlydurable at the relatively thin wall thickness (e.g., 0.009 inch to 0.013inch). Many other polyolefin materials (even other polyethylenematerials) simply cannot provide the desired high transmittance, lowreflectance, and low diffraction characteristics, particularly whilebeing sufficiently durable at that wall thickness. A suitable UHMWPEmaterial is POLY IR2, available from Fresnel Tech., located in Dallas,Tex. Although details of the POLY IR2 material are proprietary, it isbelieved to be a polyethylene copolymer, and may include additives forimproved UV stability, which is helpful where it is contemplated thatthe lens covers will remain outdoors, exposed to the environment forlong periods of time (e.g., years). Although the molecular weight of thePOLY IR2 UHMWPE material is not known specifically, it is believed to befrom about 2 million to about 6 million Daltons/mole. Such UHMWPEmaterials are very tough, with the highest impact strength of any knownthermoplastics. The number of monomers per molecule in the UHMWPE isbelieved to be from perhaps 100.000 to about 250.000, much higher thanfor high density polyethylene (HDPE). Such UHMWPE materials exhibit veryhigh strength (e.g., greater than 1 GPa, greater than 1.5 GPa, greaterthan 2 GPa, e.g., about 2.4 GPa), and density near that of water (e.g.,about 0.97 g/cm³), for very high strength to weight ratios.

The inventor attempted various unsuccessful methods of polishing of thethin-walled lens cover 112. Polishing such a thin sidewall 112 has beendescribed by the inventor as akin to attempting to polish butter, as itis very difficult to achieve the desired surface finish in such a thinsidewall without destroying the surface (e.g., wearing holes in it,causing it to buckle, crease, or fold, etc.). Conventional polishingprocedures were found to destroy the sidewall and its exterior surface.For example, it was found that buffing wheels as commonly used invarious polishing procedures will not work. Lambs wool, and clothpolishing surfaces did not work. It was found that use of a foam pad forpolishing could work, when care is taken.

FIG. 6 schematically illustrates polishing of sidewall 106 aftersanding, resulting in the finished cap structure 106 as seen in FIG. 4E.Cap structure 106 may again be placed over a mandrel 126. Whilepolishing, sidewall 112 is contacted with a rotating polishing wheelcovered with a foam pad 132. The mandrel 126 may rotate cap structure106 very slowly (e.g., less than about 10 RPM, less than about 5 RPM, orabout 3 to 4 RPM referring to arrow B), while the polishing wheel andfoam pad 132 is rotated at a much higher rate (e.g., about 1200 RPM toabout 2000 RPM, about 1500 RPM to about 2000 RPM, or about 1800 RPMreferring to arrow C). Polishing may be achieved in a two-step process,using a first foam pad and a first polishing compound, and thenpolishing with a second foam pad and a second polishing compound. Bothpolishing steps may be performed wet, with water or other lubricant. Thefirst foam pad may be differently configured than the second foam pad,and similarly the first polishing compound may be differently formulatedthan the second polishing compound.

The first foam pad may be of a coarser foam structure than the secondfoam pad. Commercially available polishing foam pads may be employed.For example, MEGUIARS soft pads have been found to be suitable for use.The MEGUIARS pads are color coded. MEGUIARS red “cutting foam pad” andthe MEGUIARS yellow “polishing foam pad” have been found to be suitablefor use as the first and second foam pads, respectively. The red cuttingfoam pad is of a coarser foam (e.g., cell size) than the yellow pad,which exhibits a finer foam structure.

Polishing compounds that are commercially available may be used with thefoam pads. The first polishing compound may include a fine grit, whilethe second polishing compound may include less, or no such grit. Forexample, an example of a suitable first polishing compound is MEGUIARSNo. 4 “heavy cut cleaner”. It includes a fine grit than can be felt whenrubbing the composition between the thumb and finger. An example of asuitable second polishing compound is MEGUIARS No. 2 “fine cut cleaner”.No grit is felt when rubbing the composition between the thumb andfinger. After polishing using the first foam pad and corresponding firstpolishing compound, the cap structure 106 (e.g., sidewall 112) may berinsed and wiped before polishing with the second foam pad and thesecond polishing compound.

Once polished, the surface 112 may exhibit higher transmittance than thesurface at FIG. 4C or 4D. The surface may still not appear transparentto the eye (visible light wavelengths), but exhibit a translucentappearance. The surface is smooth, advantageously exhibits relativelyhigh transmission to the target LWIR wavelengths of interest, lowreflection and diffraction, and does not exhibit any significant lensingartifacts, curvature artifacts, etc.

It must be noted that, as used in this specification and the appendedclaims, the singular forms “a,” “an” and “the” include plural referentsunless the content clearly dictates otherwise. In some embodiments, anyreference to thickness, other dimensions, or other numerical values mayvary by up to 10% (e.g., “about” in some embodiments may refer to ±10%,±5%, or ±3%). Substantially uniform thickness may refer to similarvariances (±10%, ±5%, or ±3%) relative to an average thickness of agiven portion.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or characteristics. The described embodimentsare to be considered in all respects only as illustrative and notrestrictive. The scope of the invention is, therefore, indicated by theappended claims rather than by the foregoing description. All changeswhich come within the meaning and range of equivalency of the claims areto be embraced within their scope.

The invention claimed is:
 1. A cap structure including a seamless lenscover, which cap structure forms a portion of a rotating camera system,the cap structure comprising: a generally cylindrical hollow bodyincluding an open bottom end, a top end, and a generally cylindricalsidewall extending therebetween; a top cap that is a separate piecerelative to the top end of the generally cylindrical hollow body, thetop cap being positioned or positionable over the top end of thegenerally cylindrical hollow body; wherein the generally cylindricalsidewall is a lens cover through which a camera of the camera systemdirectly obtains images, the cylindrical sidewall being seamless;wherein the generally cylindrical sidewall has a substantially uniformthickness that is less than 0.025 inch.
 2. The cap structure as recitedin claim 1, wherein the cylindrical sidewall has a substantially uniformthickness that is less than 0.015 inch.
 3. The cap structure as recitedin claim 1, wherein the cylindrical sidewall has a substantially uniformthickness that is from about 0.009 inch to about 0.013 inch.
 4. The capstructure as recited in claim 1, wherein the lens cover has atransmittance to a thermal spectrum of at least about 60%, exhibits noseams, no significant lensing characteristics, and no significantcurvature effect.
 5. The cap structure as recited in claim 1, whereinthe generally cylindrical sidewall includes a taper, the taper beingless than 4°.
 6. The cap structure as recited in claim 1, wherein thefinal desired cover thickness is no more than 0.014 inch.
 7. The capstructure as recited in claim 1, wherein the cap structure comprises anultra-high molecular weight polyethylene material.
 8. The cap structureas recited in claim 1, wherein the cap structure is formed from a singleintegral piece of ultra-high molecular weight polyethylene material. 9.The cap structure as recited in claim 5, wherein the taper is less than1°.
 10. The cap structure as recited in claim 1, wherein the generallycylindrical sidewall is tapered, so as to be a truncated cone shape. 11.The cap structure as recited in claim 1, wherein the generallycylindrical sidewall is not tapered, so as to be cylindrical in shape,rather than a cone or truncated cone.
 12. The cap structure as recitedin claim 1, wherein: (i) the generally cylindrical hollow body defines ahollow interior, and wherein the camera is at least partially positionedwithin the hollow interior of the cap structure, with the camerapositioned between the open bottom end and the top end; and (ii) whereinthe camera is positioned within the cap structure such that imagesobtained by the camera are obtained along a line of sight that isgenerally perpendicular to the generally cylindrical sidewall of the capstructure.
 13. The rotating camera system as recited in claim 1, whereinthe generally cylindrical sidewall is translucent, rather thantransparent.
 14. A rotating camera system including a cap structurehaving a seamless lens, the system comprising: a rotating camera that iscapable of rotation through 360°; a cap structure that serves as a lenscover for the rotating camera, the cap structure including: a generallycylindrical hollow body including an open bottom end, a top end, and agenerally cylindrical sidewall extending therebetween, the generallycylindrical sidewall being translucent rather than transparent, and thegenerally cylindrical sidewall being seamless; wherein the translucentgenerally cylindrical sidewall serves as the lens cover through whichthe rotating camera of the camera system obtains images; wherein thegenerally cylindrical sidewall has a substantially uniform thicknessthat is less than 0.025 inch; and a top cap that is a separate piecerelative to the top end of the generally cylindrical hollow body, thetop cap being positioned or positionable over the top end of thegenerally cylindrical hollow body.
 15. The rotating camera system asrecited in claim 14, wherein a top portion of the cap structure,including the top end of the generally cylindrical sidewall which iscovered by the top cap, is of a diameter that is less than the diameterof the generally cylindrical sidewall that serves as the lens cover. 16.The rotating camera system as recited in claim 14, further comprising athickened flange adjacent the open bottom end of the generallycylindrical hollow body, the thickened flange including structure forsecuring the cap structure to an adjacent portion of the camera system.17. The rotating camera system as recited in claim 16, wherein thethickened flange is outwardly flared, extending radially outward fromthe bottom end of the generally cylindrical sidewall.
 18. The rotatingcamera system as recited in claim 16, wherein the structure for securingthe cap structure to an adjacent portion of the camera system comprisesthreads.
 19. The rotating camera system as recited in claim 16, whereinthe outwardly flared flange further includes an annular groove intowhich a sealing o-ring is positioned or positionable.